1. Field of the Invention
The present invention relates to a wireless power supply technique.
2. Description of the Related Art
In recent years, in order to supply electric power to an electronic device, contactless power transmission (which is also referred to as “contactless power supply” or “wireless power supply”) has begun to come into commonplace use. In order to advance the compatibility of products between manufacturers, the WPC (Wireless Power Consortium) has been organized, and the WPC has developed the Qi standard as an international standard.
FIG. 1 is a diagram showing a configuration of a wireless power supply system 100 that conforms to the Qi standard. The power supply system 100 includes a power transmitter 200 (TX) and a power receiver 300 (RX). The power receiver 300 is mounted on an electronic device, examples of which include cellular phone terminals, smartphones, audio players, game machines, and tablet terminals.
The power transmitter 200 includes a transmission coil (primary coil) 202, a driver 204, a controller 206, and a demodulator 208. The driver 204 includes an H-bridge circuit (full-bridge) circuit or otherwise a half-bridge circuit. The driver 204 applies a driving signal S1, which is configured as a driving current or otherwise a driving voltage, to the transmission coil 202 such that the transmission coil 202 generates an electric power signal S2 in an electromagnetic field. The controller 206 integrally controls the overall operation of the power transmitter 200. Specifically, the controller 206 controls the switching frequency of the driver 204 or otherwise the duty ratio of the switching operation of the driver 204 so as to adjust the electric power to be transmitted.
In the Qi standard, a protocol is defined for communication between the power transmitter 200 and the power receiver 300, which enables information transmission from the power receiver 300 to the power transmitter 200 via a control signal S3. The control signal S3 is transmitted from a reception coil 302 (secondary coil) to the transmission coil 202 in the form of an AM (Amplitude Modulation) modulated signal using backscatter modulation. The control signal S3 includes electric power control data (which will also be referred to as a “packet”) which indicates an amount of electric power to be supplied to the power receiver 300, and data which indicates the particular information for the power receiver 300. The demodulator 208 demodulates the control signal S3 included in the current or otherwise the voltage applied to the transmission coil 202. The controller 206 controls the driver 204 based on the power control data included in the control signal S3 thus demodulated.
The power receiver 300 includes the reception coil 302, a rectifier circuit 304, a capacitor 306, a modulator 308, a load circuit 310, a controller 312, and a power supply circuit 314. The reception coil 302 receives the electric power signal S2 from the transmission coil 202, and transmits the control signal S3 to the transmission coil 202. The rectifier circuit 304 and the capacitor 306 rectify and smooth a current S4 induced at the reception coil 302 according to the electric power signal S2, thereby converting the current S4 into a DC voltage.
Using electric power supplied from the power transmitter 200, the power supply circuit 314 charges an unshown secondary battery or steps up or otherwise steps down the DC voltage Vdc, so as to supply the DC voltage to the controller 312 and other load circuits 310.
The controller 312 monitors the amount of electric power received by the power receiver 300, and generates electric power control data which indicates the amount of electric power thus supplied. The modulator 308 modulates the control signal S3 including the electric power control data so as to modulate the coil current that flows through the reception coil 302, thereby modulating the coil current and coil voltage applied to the transmission coil 202.